FIG. 1 is a cross section showing a semiconductor package described in Patent Document 1. A semiconductor package 200 shown in FIG. 1 includes a semiconductor device 206, a flexible substrate 208 (also called “interposer substrate”) disposed so as to surround the semiconductor device 206, and at least one inserted plate 207 disposed around the semiconductor device.
On the under face side in the diagram of the semiconductor device 206, a circuit face is formed. An external electrode is formed on the circuit face. The inserted plate 207 is used mainly as a spacer, is made of, for example, a metal material, formed in thickness equal to that of the semiconductor device 206.
On the flexible substrate 208, a wiring pattern 205 connected to the external electrode of the semiconductor device 206 is formed. One side or both sides of the wiring pattern 205 is/are covered with thermoplastic insulating resin layers 203 and 204.
Concretely, the semiconductor device 206 and the wiring pattern 205 are electrically connected to each other via conductor bumps 202. On the under face side of the flexible substrate 208, the resin layer 203 is partially removed, thereby providing parts (electrode pad) from which the wiring pattern 205 is exposed. Solder balls 201 are disposed in the parts. The semiconductor package 200 constructed as described above is mounted on a secondary mounting board (for example, mother board) via the solder balls 201.
The configuration that the pitch of the conductor bumps 202 on the side of the semiconductor device 206 is wider than the pitch of the solder balls 201 is also called a “fan-out type” and has the following advantages. Since the technique of narrowing the pitch of external terminals on the secondary mounting board side does not sufficiently catch up with a semiconductor device shrinking technique (outer-size reducing technique) at present, the pitch of external terminals on the secondary mounting board side is wider than that on the semiconductor device side. Therefore, in order to compensate the difference in the pitches, the flexible substrate 208 is used to increase the pitch of the external terminals.
In the package structure of the fan-out type as shown in FIG. 1, external terminals (electrode pads) are formed on the top and under faces of the package. Consequently, it is also possible to stack the package on another package to obtain three-dimensional mounting.    Patent Document 1: Japanese Patent Application Laid-open No. 2004-172322